Impedance transformer



April 5, 1948- w. w. HANSEN yxs-r AL 4 Sheets-Sheet 1 IMPEDANCE TRANSFORMER Filed June 29, 1942 AToRNEY April 5, 1948. w. w. HANSEN. Er AL. 2,438,912

IMPEDANCE TRANSFORMER Filed June 29, 1942 4 sheets-sheet 2 April 6, 1948. w. w. HANSEN ET AL IMPEDNCE TRANSFORMER 4 sheets-sheet s Filed June 29, 1942 Liam) April 5, 1948' l w..w. HANSEN Er AL A 2,438,912

I IMPEDANCE TRANSFORMER FIG. 9

RLEWSISEN H R.wo' DYARD MoRms-RELSON A BY f ATTORNEY Patented Apr. 6, 1948 TMPEDANCE TRANSFORMER William W. Hansen and John R. Woodyard, Garden City, and Morris Reisen, Kew Gardens, N. Y., assigner: to The SperryCorpoi-ation, a-

cci-poration of Delaware Application Juno 29, 1942, Serial No. 448,992

I 17 claims.

The present invention relates to the art including impedance matching and transforming devices especially adapted for use in systems utilizing high frequency electromagnetic energy.

In transferring energy from one high frequency device to the other, it is well known that the impedances thereof must .be properly matched in order to avoid the production of provision of improved impedance matching and transforming devices which are adapted to eiliciently couple and match any two arbitrary impedances, and to transform any arbitrary im-` pedance into any other arbitrary impedance, with a minimum of adjustment and a maximum facility and efllciency.

According to the present invention, such impedance transformers are provided of the concentric line type having fixed physical length whereby they may readily be manufactured and permanently and rigidly connected into a system. Conoentric line impedance transformers have been disclosed in Hansen and Woodyard Patent No. 2,406,372 granted August 27, 1946. In such devices, it is known that by the provision of only a single adjustment, avery restricted range of transformation is obtained. By providing three adjustments, any desired transformation may be obtained, but the practical difficulties of making three simultaneous interdependent adjustments renders such devices of limited utility. When using two adjustments.

Vthe range of possible transformations is inof the device, and by the use of special contactresistance-reducing means useful wherever sliding contact is required.

. t 2 Accordingly, it is an object of the present invention .to provide improved impedance matchingctransformers for matching any two arbitrary impedances.

l ,ItA is another object of the present invention toqprovide improved-impedance matching transstanding waves with attendant increase in lossfarmers of nxed effective length suitable for rigid connection in a system.

It is still another object of .the present invention to provide improved impedance transformers having a minimum number of adjustments and a maximum range of transformations.

It is a further object of the present invention to provide improved impedance matching trans` formers including high efficiency joints therein for reducing the effects of sliding contact.

It is a still further object of the present inventionto provide vimproved sliding joints for concentric transmission line devices.

It is another object of the present invention to provide improved means for adjustably connecting one concentric transmission line in shunt with a second.

Further objects and advantages of the present invention will become apparent from the following specification and drawings, in which,

Fig. l shows a longitudinal cross-sectional view partly in elevation of one form of the present invention:

Fig. 2 shows an enlarged cross-section of a detail of the device of Fig. 1 taken along line 2-2 thereof;

Fig. 3 shows an enlarged elevational view of a detail of the device of Fig. 1 taken along line 3-3 thereof;

Fig. 4 shows an admittance bipolar coordinate -or circle diagram useful in explaining the theory of operation of the device of Figs. 1 3;

Fig. 5 shows a longitudinal cross-sectional view partly in elevation of a modified form of the 1- invention;

Figs. 6A and 6B show impedance bipolar coordinate or circle diagrams useful in explaining the theory of operation of the device of Fig. 5:

Fig. "l shows a similar cross-sectional view of still another modification of the invention;

Fig. 8 shows a longitudinal cross-sectional view of still another embodiment of the invention; and

Fig. 9 shows an admittance circle diagram` useful in explaining the theory of operation of the device of Fig. 8.

Referring to Figs. 1 to 3, there is'shown one form of impedance transformer adapted to elllciently couple and match two arbitrary impedsulating discs I1, I3 may be provided at suitable points along the length of line section I2 as required by considerations of mechanical support. Preferably, however, spacers are placed in pairs having their centersspaced apart by a distance electrically equivalent to a quarter wavelength or 90 electrical degrees of the operating frequency. By so doing, the effect of these insulating spacers, due to the discontinuity they present in the dielectric medium within line section I2, is greatly minimized, and standing waves caused thereby are substantially eliminated.

Thus, considering for example an electromagnetic Wave travelling from left to right down line section I2, such a wave would meet a dielectric discontinuity at the spacer |1 and `a portion of l v'this wave" will be'"reected thereby. Another portion of the wave will be transmitted further to the right and will be reflected by spacer I8. These two reected waves will be superposed in the portion of the line section |2 to the left of spacer I1. Since spacers I1 and I8 have been placed a distance apart equivalent to a quarter wavelength, the wave reilected by spacer I8 will be a half-wavelength or 180 out of phase with respect to the wave reflected by spacer I1, and these two waves will tend to neutralize and cancel one another. In this Way, the electrical effects of such insulating spacers, which are necessarily present because of the mechanical considerations of the device, are minimized and substantially eliminated.

The impedance transformer II of Fig. l is adapted to provide an adjustable short-circuited stub transmission line section in shunt with the concentric line sections I2 and I3, the point of connection of this shunt line section with the concentric line sections l2, I3 being made longitudinally adjustable along -line sections I2, I3. For this purpose, inner conductor |4 of line section I2 and inner conductor I9 of line section I3 are joined by a conductor 22 which together with a tubular outer conductor shell 23 movable on concentric line sections I2 and I3 form a central concentric transmission line section joining line sections I2 and I3 in cascade.

Conductor 22 is made of larger diameter than inner conductors I4 and I9, and is joined to them at each end by respective tapered portions 24 and 25. The diameters of inner conductor 22 and outer conductor 23 are so chosen that the characteristic impedance of the transmission line section 22, 23 will be equal to that of line sections I2, I3. In order to join line sections I2 and I3 smoothly and without reflections or mismatch to line sections 22, 23, respective internally tapered portions 26, 21 are attached to outer conductors these insulating I6 and 2| of line sections I2 and I3. The internal tapers of portions 26 and 21 are so selected and are so placed relative to tapered portions 24, 25 of inner conductor 22, that the ratio of inner conductors I4, 24, 22, 25, I9 lto the respective outer conductors I6, 26, 23, 21. 2| remains uniform and constant for the entire length of the impedance transformer II, thereby assuring a uniform characteristic impedance and substantially no reflections or mismatch which might provide undesirable standing waves with consequent reduced eiliciency and other attendant disadvantages.

The internally tapered portions 26. 21 are provided with cylindrical outer sirfaces 26, 29 having a diameter just slightly smaller than the internal diameter of tubular outer conductor shell 23 whereby portions 26 and 21 do not contact shell 23, and shell 23 may be easily slid along the device. To provide electrical contact between outer conductor shell 23 and outer conductors I6, 26 and .-21, 2| to complete the main line section oi' the device, connecting discs 3| and 32 are provided fastened to outer conductors I6 and 2| and provided at their peripheries with spring fingers 33:. and 34 .extending peripherally therearound and adapted to form'good electrical contact wit shell 23.

In this manner, shell 23 may be axially displaced along line sections I2, I3 without in any way changing the electrical properties of the cascaded line sections I4, I6; 24, 26; 22, 23; 25, 21; and I9, 2|. In order to provide efficient electrical contact between shell 23 and the stationary outer y"crinductorsfoif theseI lines it-is most Vdesirablethat very low resistance appear at the innermost points |0I, |02 of the internally tapered portions 26, 21, which are the points at which the electric currents flowing along the composite outer conductor of the device would effectively cross over from outer conductor 2| or I6 to shell 23.

y For this purpose, the axial length of the cylindrical outer surface of each of the tapered sections f 26 and 21 is made to be electrically exactly a quarter wavelength of the operating frequency, and their outer diameters are selected to be as nearly equal tothe inner diameter of shell 23 as possible without obtaining direct mechanical contact. In this way, sections 26 and 21 form quarter wavelength low impedance concentric transmission line sections with outer conductor 23. Furthermore, the spacing between the outermost edges such as 36, 31 of portions 26, 21 from the innermost surfaces 38, 39 of Vcontacting discs 3|, 32 is also made tovbe electrically equivalent to a quarter Wavelength of the operating frequency whereby a second quarter wave section of concentric transmission line is formed by shell 23 serving as outer conductor, and conductors I6 and 2| of line sections I2, |3 serving as inner conductors. In order to make the characteristic impedance of the latter quarter-wave sections as large as possible, the outer diameter of conductors I6 and 2| is reduced by thinning the wall thickness thereof, whereby the impedances of these sections is increased without aiecting that of line sections I2 and I 3.

It will be seen thatthe quarter Wave line section I6, 23 is short-circuited at the left by disc 3|, this short-circuit being produced by the low radial resistance of disc 3| in series with the contact resistance between lingers 33 and outer conductor 23. This fairly low impedance will be transformed by the high impedance line section I6, 23 to a high impedanceat point 36 having the value where Z is the characteristic impedance of line section I6, 23 and R is the short-circuiting resistance. It will be noted that this value'will be extremely high due to the low value` of resistance R and to the high'value of the characteristic impedance Z.` l

By the action of the low impedance quarter wave line section 26, 23 this high impedance is transformed to a low impedance having the value at the innermost end |62 of tapered section26, where Z is the characteristic impedance of line section 26, 23. Since Z is much smaller than Z, it will be clear that the effective gapresistanc'e at the innermost point |02 of tapered portion 26 will be much lower than the contact resistance between fingers 33 and sleeve 23, and in this mannera highly eflicientand extremely low'resistance sliding joint between outer conductor I6 and 23 is provided. If desired-further alternately high and low impedance quarter wave sections tor. Accordingly, the length of 'plate 41 along the x axis of conductor 22 is preferably made substantially equal to a half wavelength, although it may be less if desired. Intthis manner, the line section 43'may be axially adjusted in position along `the line section 22, 23, an efficient connection bein'gprovided by themeans just described.

Preferably the length of slot 44 in conductor 22 is inade of such length that at least a halfwavelengthof adjustment of the point of connection 45 between line sections 43 and 22, 23 may be provided. l f

' i In orderto suitably adjust the length of line formed similarly to.I6, 23 and 26, 23 may l be inserted here to further decrease the ultimate gap'resistance. y u

.Asdescribed above, line section I6, 23 forms a quarter-wave section short-circuited at the left by disc 3l and fingers 33. As is well-known, such a line section has a current anti-node or-loop at the shorting point, resulting in relatively high current intensity. This high vcurrent flowing through the contact resistance of fingers 33 would produce high losses. To minimize these losses, fingers 33 are made of substantial length relative to a quarter wavelength of thel operating fre- -quency whereby the actualsliding contact occurs at a point of lower current intensity, thus reducing losses andheating.

It will be clear that the same type of joint is provided between outer. conductor 2I` and sleeve 23.

In order to adjustably insert a shunt section of concentric transmission line I I, shell v23 is connectedperpendicularly'to an outer conductor 4I which cooperates with an inner conductor 42 to provide a concentric transmission line section 43. To connect this line section 43 in shunt with line section 22, 23 it is necessary to connect inner conductor 42 to inner conductor 22. However, as described above, it is also desired to adjust the point of connection of line section 43 with respect to concentric line section 22, 23.

For this purposey conductor 22 is formed with a longitudinally extending slot 44 shown more clearly in Figs. 2 and 3. The end of conductor 42 is provided with an internally circularly rounded portion 46 for cooperation with conductor 22 to provide an extremely 'small gap between conductors 22 and 42. suitably fixed to inner conductor 42, as by soldering, etc., is a flat metallic plate 41 extending axially of conductor 42 and within the slot 44 of conductor 22. In this manner, conductors 22 and 42 may be connected in high frequency fashion through the large capacitance formed by the small arcuate gap between conductors 22 and 42 and by the small gap between plate .sectionv 43, a slidable plunger 5I is provided hav- `ing a shorting` disc 52 provided with two sets of `spring ngers 53, 55, andthereby serves to interconnect the inner conductor 42 and outericonductor 4I through a, fairly low resistance. In

xorder to'still further reduce this contact resistance.. impedance transformer lmeans are provided Y similar to that describedwith'respect to the sliding jolnt"between conductors I6, 2| and sleeve 23.

-For this purpose, a cylindrical shell 541s suitably fastened toshorting disc 52, and -concentrically thereof. At l-theopposite end, shell 54 is connected to an annular disc 56 whichisspaced onlyslightly from inner conductor 42 and from outer conductor 4I `-bysuitable thin rings of dielectric-material. such as 51 and 58. The length of cylindrical shell 54 'as' measured Vbetween the inner face59 ofl plunger 52 and the outer face 6I of annular disc 56 is selected tofbe electrically equivalent to a quatrer wavelength of the oper- 'ating frequency. The axial thickness of disc 56 is also chosen to be electrically equivalent to a quarter wavelentgh. Since dielectric materialls provided' between disc 56 and both inner conductor`42 and outer conductor 4I, the physical length required for conductor 56 will be substantially less than a quarter wavelength in free space. In this manner, shell 54 and outer conductor 4I form a high impedance quarter-wave line sectin short-clrcuited at the outer end by the contact resistance between fingers 53`and outer conductor 4I. This line section is in cascade with the low impedance quarter-wave section 56, 4I, whereby the contact resistance between disc 52 and conductor 4I is transformed to point 62 "as a much lower resistance in the. manner already dei much lower resistance at point 63. In this way,

41 and conductor 22. In `order to increase and maintain this capacitance substantially constant, a pair of dielectric plates 43, 49 are preferably ter-wave line sections forming the contact re-v sistance transformer have as high a ratio as possible in order to provide the lowest transformed I contact resistance. For line section 54, 4I this would necessitate the smallest possible outer diameter of shell 54. However, for line section 54, 42 this would necessitate the largest possible innermost diameter of shell 54. Since these two conditions are mutually exclusive, and since the net contact resistance provided by annular disc 5B is the sum of the resistances reflected at points 62, 63, which is to be minimized,shell 54 is made to be as thin as possible and its inner and outer diameters are so chosen that the characteristic impedances of line sections 42, 54 and 54, 4I are substantially equal. This requires that the average diameter of shell 54 be substantially the geometric'means between the diameters of inner conductor 42 and outer conductor 4|. In this manner a minimum effective contact resistance is obtained.

In order to suitably adjust the position of shorting plunger 56 along line section 43, several thrust rods are provided, of which two, namely, 64 and 66, appear in the section taken. These rods are fastened to disc 52 and are movable axially of line section 43 by means of a suitable screw 61 threaded into member 6B, to which rods 64, 66, etc. are also fastened. In this manner, both the length of the line section 43 and its point of connection in shunt with the concentric line formed along the major axis of the device may be suitably adjusted, and by so doing the arbitrary impedance connected at the. end of one of line sections I2 and I3 may be properly and efficiently transformed to any other impedance value at the.-end of the other line section I3 or I2. It will be clear that any other suitable adjusting means may be used.

The operation of the device of Fig. 1 may be explained by reference to Fig. 4 which shows an admittance diagram having coordinate axes representing conductance g and susceptance b, as

shown. Point Yo on this diagram represents the common characteristic admittance of line sections 22, 23; I4, I'li and I9, 2l.

vIf an arbitrary admittance represented by point Y1 is connected to an adjustable length transmission line section having characteristic admittance Yo, it may be shown that the admittance Y1', looking through the line section toward Y1, may be represented by the equation where 11 and p are quantities dened by and Here :c is the length of line in wavelengths, G1 is the conductance of Y1 and B1 is the susceptance of Y1. Graphically, the locus of resultant admittance Y1 as :c varies is given by the circle defined by setting ,l equal to zero, which may be termed a bipolar coordinate circle having Yo as pole. Such a`ci1'cle is shown at 'I0 in Fig. 4. For each added half-wavelength of line, one com- 'plete traverse of circle 'i0 is made by Y1'.

Accordingly, if an admittance Y1 is connected to one end, say the left end, of the transformer of Fig. 1, the resultant admittance Y1 looking left from the tap point 45 will vary clockwise from 8 Y1 along circle 'III as the tap 45 is moved from left to right.

If it is desired to produce a transformed admittance Y: at the right end of transformer Il, then the admittance Yn' at point 45 looking to` the right, which is required to produce Y: at the end of the line section I3, will lie somewhere on the bipolar coordinate circle 1I passing through Ya, but displaced counter-clockwise from Yz, de` pending on the position of point 45. As tap 4B moves rightward, Y2' also moves on circle 1I clockwise about Yo. Since one of these circles 'l0 is completely within the other circle 1I. it will be clear that for some particular setting of the Junction 45, Y1' and Y2' will be one directly above the other; that is, they will differ only by pure susceptance. Such a position is shown by Y1" and Y2" in Fig. 4. l

When such a position is found, the admittance Y2 and therefore the desired transformed admittance Y2 at the right end may he produced by adjusting the position of plunger 5I to add or subtract the required amount of susceptance to admittance Y1". In this manner any arbitrary admittance Yrcat one end of transformer Il may be transformed into any other arbitrary' admittance Y2 at the other end.

Since in practice the condition of matching or proper transformation is most usually tested by observing the standing wave'ratio or power output, it will be clear that these two adjustments, namely that of the position of the Junction point 45 and of the position of plunger 52, must be made by trial and error to produce the desired result. Usually this will be done by setting one of these values to an optimum position, which generally will not be the desired condition, and then resetting the other to improve upon this optimum condition. Thus by alternately resetting each of the two adjustable portions of the device, the proper transforming condition can be obtained after only a few manipulations.

Fig. 5 shows another type of impedance transformer also adapted to efliciently match two arbitrary impedances. In this instance, transformation is performed by adding a concentric line section serving as an adjustable reactance in series with the arbitrary impedance to be transformed, then, effecting a transformation by a quarterwave section of line, and adding further adjustable reactance, to derive the desired transformed impedance.

In general, this will not permit the transformation of any impedance at one end to any other impedance at the other end. However, by adding a quarter-wavelength more of concentric transmission line at one end than at the other, any transformation may be obtained if care is taken to connect the impedance element to be transformed at the proper end, as will be shown below. In this manner, the transformer may remain of fixed length,and any transformation may be obtained by adjustment thereof and a possible reversal or turning over of the device.

Thus, referring to Fig. 5 and considering for the moment only the left-hand half, which is substantially duplicated on the right side, there is provided a fixed concentric transmission line end section 8l' comprising an inner conductor 82 and an outer conductor 83 of any suitable relative diametersadapted to provide a convenient characteristic impedance. This transmission line section 8l may -be suitably formed at its end to provide a convenient coupling with other concentric transmission line devices, as described in?" 83. Supported on outer conductor 83 by means of an annular .disc 88 is a concentric sleeve 81. Sleeve 81 and outer conductor 83 are then adapted to form awfurther concentric transmission line section. A snorting device for ccnductively connecting sleeve 81 and conductor 83 is provided in the form o! a movable annular piston or plunger 88 adapted to be moved by axial actuation of acontrol ring 88 fastened to plunger 88 by means of a plurality of rods 8i which pass through suitable openings 82 in the annular, supporting disc 88. Any other type of control for plunger 88 may be used here.

Plunger 88 is provided with a plurality of spring fingers 88 which provide a rubbing or sliding contact with'the inner surface oi' sleeve 81. Fingers 93 are preferably spaced from the inner wall of sleeve 81 except at their ends 84 which are in sliding contact therewith. Fingers 83 extend completely around within sleeve 81, forming a substantially complete cylinder with axial slits to form the several fingers. The overall-length of fingers 83 including tips 84 is preferably chosen to be substantially a quarter wavelength, to improve the electrical characteristics of the sliding joints of these points.

Thus, it will be seen that the nngers 83 form located, provides a current node at which minimum current exists. Accordingly, by having slidin'g contact only at tips 84, it will be clear that such contact and'its inherent contact resistance occurs at points of low current intensity, where- `by undesirable losses are minimized. It will be in the circuit. The same condition can be seen from the fact that at the right end of each of these lines. the electric vectors, which are normally radial, are effectively in series and therefore the two transmission line sections are in series.

This is in marked distinction to two other usual types of connection of transmission lines, namely, a shunt connection and a cascade connection. Both oi' these other types are illustrated in Fig. 1. For example, transmission line section 22, 23 is in shunt with line section 4i, 42, since the inner conductors 42, 22 and the outer conductors 23, 4| thereof are respectively joined together and to the corresponding conductors of the 'output circuit comprising transmission line section I3.

However, transmission lines 22, 23 and 1|9, 2i are effectively in cascade since their respective conductors are connected together and energy ows lccessively through these transmission line secons.

The right-hand portion of the impedanceV matching device of Fig. is substantially identical 4a quarter wave concentric transmission line secseen that where the current is a. maximum no sliding contact exists, since plunger 88 isy solidly connected to fingers 83. A similar construction is provided for ilngers 88 having contacting tips 811 It will be clear that the type of sliding contact between plunger 88 and sleeve 81 or conductor 83 has no eiect upon the electrical characteristics of the system, but is merely useful to provide smooth actuation and variation in position of plunger 88 with respect to the rest of the e device.

ly connected tothe inner conductor 83 of the ilrst of those` line sections while the output from both lines is taken from the inner conductor 82 ofthe second line and the outer conductor 81 of the rst line. Hence a true series circuit is provided since currents flowing along the outer conductor 83 must successively traverse both conductors of line section 83, 81 before continuing with that already described, having an'end section 82, 83' terminating at point 84 in series with aline section 83', 81' adjustable by means of movable plunger 88'. Section 82, 83 is chosen of a length differing from that of 82, 83 by an odd multiple oi.' a quarter-wavelength.

The space between points 84' and 84 is occupied by` a concentric line section comprising an outer conductor 88 having inner diameter substantially identical to the common inner diameter of outer conductors 83 and 8 5 and connected to conductors 81 and 81', and an inner conductor formed by conductor 82. Outer conductor 88 is -made of a length to provide a very'narrow gap 88 between it and line section 82, 83, and a very this causes conductor 88 to cooperate with inner conductor 82 as a quarter-wave transmission line section.

The operation of the device of Fig. 5 mayibe explained by reference to Figs. 6A and 6B. Thus, referring to Fig. 6A, there is shown an impedance diagram having 1' and :c coordinate axes, and showing a family of b-polar coordinate circles having the common characteristic iin-` pedance of Zo of lines 82, 83; 82, 83' or 82, 88 as the pole thereof. It an arbitrary impedance Z having resistance R and reactance X is connected to one end of the impedance transformer, for example, the right end, and if the length of line section 82, 83' is assumed as an even multiple of a quarter Wavelength of the operating frequency. then the impedance looking toward the right from point 84' will also have the value Z. To this impedance Z the short-circuited seriesconnected transmission line section 83',- 81' adds an adjustable amount of pure reactance, so that, looking right from point 8i', there may be obtained any impedance whose value can be represented by a point on line AB. The quarter-wave section of the transmission line 82, 88 will then vtransform each point of line AB to a corresponding point of circle OCD. It is to be' understood` 1l to the point R at which line AB crosses the r-axis. Point C will then represent an impedance le A traversal of line AB in the direction of the arrow will produce a traversal of circle ODC in a clockwise sense, as shown.

'I'he second short-circuited series-connected transmission line section Il, 81 then adds an adjustable amount of pure reactance to whatever impedance is seen at point 85, namely, it adds adjustable reactance to any point of circle OCD. Consequently the locus of all impedances into which the impedance Z may be transformed by the present device, as so far described, will'be contained within the strip bounded by the -axis and the line ECF parallel thereto. It will thus be seen that unless special provision is made, an arbitrary impedance Z cannot be transformed into any other arbitrary impedance by the present device.

In order to permit such arbitrary transformation, the line section 82, 83 may be made to have a length equal to an odd multiple of a quarter wave length. This performs a further transformation of impedance such that each point of the strip contained between the :i1-axis and line EF is transformed into a corresponding point of the positive Z plane outside circle OHR, and consequently, for this device, an arbitrary impedanoc Z may be transformed into any other impedance whose corresponding plot is not contained within the circle OHR.

This condition may be also stated in the form that, if the transformed impedance is denoted by r G R of the transformed impedance Z' has a value no greater than the reciprocal of the resistance R of the arbitrary impedance Z.

In order to overcome this restriction on the range of transformation, itis merely necessary to connect the opposite end of the impedance transformer of Fig. 5 to the arbitrary impedance Z to be transformed. Thus, referring to Fig. 6B, if the arbitrary impedance Z is connected to the left end of the impedance transformer of Fig. 5, then the line section 82, 83, being of length equal to an odd-multiple of a quarter-wavelength, will fbe transformed to another impedance, such as Z, located on the same bipolar coordinate circle as impedance Z. The series-connected short-circuited, transmission line section 83, 81 then adds an adjustable amount of reactance to this impedance Z, whereby the impedance seen at point 85 may be adjusted to have any value corresponding to points along line AB. The quarterwave section 82, 98 then transforms each pointA of line AB into a corresponding point of circle OCZ. It will -be lclear that this circle will pass through the point Z since, if zero reactance is added by the short-circuited series-connected section 83, 81, then the impedance Z will be effectively connected in series with a half-wave line or multiple thereof, comprising cascaded sections 82, 83 and 82, 88, which would leave this impedance Z unchanged.

The second series-connected short-circuited section 83', 81 adds an adjustable amount of l2 pure reactance to the impedance seen at point 85'. and accordingly any transformed impedance whose plot is contained within the strip bounded by the axis and line ECF may be obtained by these two adjustments. This impedance remains unchanged by half-waveline 82, 83'. It may be,

shown that the width of this strip is equal to the reciprocal of the conductance of the original arbitrary impedance Z, and accordingly, with the present connection, any arbitrary impedance Z may be transformed into any other arbitrary impedance Z so long as the resistive component R of the transformed impedance Z is equal to or less than the reciprocal of the conductance of the original impedance.

It will be seen that the locus of possible transformations shown in Fig. 6B overlaps the locus of impossible transformations of Fig. 6A, and accordingly between the two Iany impedance may be transformed into any other impedance, it being necessary merely to reverse the connections to the impedance transformer for transformations within particular ranges.

Although the impedance transformer of Fig. 5 has been described in` such manner that one line section 82, 83 is an odd multiple of a quarter wavelength andthe other section 82, 83' is an even number of quarter wavelengths long, it is to be understood that the only necessary condition is that these sections shall differ by one-quarter wavelength, and it is not necessary that they be exact multiples of a quarter wavelength. If these sections depart from exact multiples of a quarter wavelength, the above ,theory still applies, but it is to be understood that the arbitrary impedance to be transformed will now differ from the impedance Z shown in the diagram by an amount corresponding to the amount the lengthI of transmission line connected thereto differs from a multiple of a quarter wavelength, and that the ultimate transformed impedance will diii'er from the value Z' found from the diagrams of Figs, 6A and 6B by an amount corresponding to the length of transmission line connected thereto. In effect,

impedances Z and Z' of the diagram yare those at points 84 and 84'. Otherwise the same theory holds and the same results may be produced.

Furthermore it is not necessary, although it is desirable, that line section 82, 98 be exactly a quarter-wave section. Any other length, excluding a half-wavelength and multiples thereof, may be used, but odd mutliples of 'a quarter-wavelength yield the most easily adjustable device, avoiding undesirable resonance conditions in th'e adjustable sections which make the transformed impedancer value highly sensitive to small adjustments.

Fig. 7 show-s a further modification of the impedance-transformer of the present invention. In this modification, two adjustable shunt concentric line sections III and II2 are provided connected to the main concentric line section I I3 at points II4 and IIS spaced by a quarter-wavelength. The arbitrary impedance to be transformed may be connected at one end of th'e main concentric line section I I3 of the device.

The line sections III and II2 are made adjust able by the use of adjustable short-circuiting plungers III and II8 of the same type as those used in Fig. 5. Preferably the length of the central line section II3a to the left of point I I4 is made to differ from the length of section II3b to the right of point I I6 by a quarter-wave-length' to that shown in Fig. 5.

terms occur in the explanation or in the dia.

grams.. With these changes, and applying the explanation to admittance diagrams similar in all respects `to those shown in Figs. 6A and 6B, it will be clear that the transformer of Fig,` 7 may transform any impedance into any other impedance so long as the `proper choice of connections to the transformer is made.

In Fig. '1 also, it is not absolutely necessary, but is desirable, that th'e separation between the shunt sections be exactly a quarter-wavelength. The quarter-wave condition yields the best operation.

In both Figs. and 7, the length of travel of the plungers which is actually employed is in no way critical but to utilize the widest range of the instrument, this length should be at least a halfwavelength in each embodiment of the invention.

Fig. 8i shows another form of impedance transformer adapted to transform an arbitrary impedance into any other impedance. The transformer of Fig. 8 comprises a main section of concentric transmission line |2| and three stub transmission line sections |22, |23 and |24 connected in sh'unt thereto, the points of connection |26, |21 and |28 thereof being positioned at quarter-wave-length intervals along the main line section |2|. Each 0f these shunt sections |22, |23 and |24 is made adjustable in length by means of respective adjustable short-circuiting pistons |29, and |3i, preferably of the same type as described with respect to Figs. 5 and 7. The central shunt section |23 may be adjusted by translation of av suitable control |32 connected to piston |30. Pistons |29 and |3| are simultaneously equally adjustable by means of a common control member |33 suitably connected thereto.

The theory of operation of the device of Fig.8 may be explained by reference to th'e admittance diagram of Fig. 9, upon which are shown the bipolar coordinate circles corresponding to the pole Yo representing the characteristic admittance of the main concentric line section |2| of the impedance transformer.

Letv it be assumed that an arbitrary admit` tance Y1 is connected to one end of the impedance transformer. for example. the right end. section of th'e main concentric transmission line section 2| to the right of point |26 will transform this admittance Y1 into a further adaccordingly, the locus of all admittances obtainable when viewing to the right from a point just to the left of junction |28 may be represented by the line AB. The quarter wave section of line between points |26 and |21 will transform points on this line AB into corresponding points on circle OYiC with a one-to-one correspondence between the points of line AB and the points of this circle. Thus, to point Y1' will correspond the point Y1, and to the point B1' representing the conductiveV component of admittance Y1' will correspond point C having a value If the susceptance added to admittance Y1' by shunt section |22 is assumed tobe of the sense as to vary Y1 upward in the direction of the arrow, then the corresponding points on the circle will move in a clockwise direction as shown and accordingly, just to the right of point |21 there may be obtained any admittance represented by points on this circle. 1

Since the variationv of shunt sections |22 and |24 occurs simultaneously by virtue of the ganged adjustment of Athese two sections, it will be clear that as susceptance is added to Y1' to vary it in the direction of the arrow, the admittance required just to the right of point |28 to produce Y2 at the left end of the device will vary oppositely from Y2 as shown by its corresponding arrow, and accordingly, the locus of the required admittance Y2 will vary along line DE in correspondence with the variation of Yi' along' AB. The quarter-wave section-between points |22 and |21 will change the value Y2' required at point |28 to the value Y2" required just to 'the left of point |21 to produce Y2 at the left end of the transformer.

As Y2' moves downward, Y2" will move in a counter-clockwise sense about circle OFYc". Since one or the other of these two circles OY1"C and OFY"2 will be within the other, and since for a given sense of adjustment of the ganged pistons |29, |3| the correspondingl loci of the transformed and required admittances at point |21 will move oppositely along these circles, it will be clear that for some particular adjustment of the ganged pistons |29, |3I, depending upon the mittance Yi looking to the right from point |26. l

It will be noted that Y1' is displaced from Y1 along the bipolar coordinate circle |35' passing through Y; by an amount corresponding to the length of the concentric line section |2| to the gram of Fig. 9, being displaced from Y: along the bipolar coordinate circle |36 'passing `therethrough, by an amount corresponding to the lengthpf the line section |2| to the left` of point |28.

n The shunt section |22 will add an adjustable 'amount of susceptance to the admittance Y1' and,

value of the arbitrary admittance Y1 and the required admittance Y2, their corresponding transformed values Y1 and Y"2 will be vertically displaced with respect to one another on the diagram of Fig, 9. At such a position, it would require only pure susceptance to pro-duce the required transformation. This pure susceptance may be produced by adjustmentof the central piston |30 to the proper position, and there,- by the arbitrary ladmittance Y1 its fully transformed to the required arbitrary transformed admittance Y2.

Although the spacing of junction points |26, |21, |28 and has been described as a quarter-wavelength, it is to be understood that this is an optimum figure only, and may be varied if desired.

Throughout this description, wherever the electrical length of a quarter or half-wavelength are used, it is to be understood that a'n lodd mul# tiple or an even multiple, respectively, of aquarter-wave-length may be used equally'as well."

vWherever the term' electrical length isV used in the present specication, it is to be understood as meaning a physical length of such value as to give the same electrical eilect as a physical length equal to the electrical length would yield in free space. All wavelengths are referred to waves in free space'.

All distances referred to in terms of wavelength are intended to be electricallengths as defined above.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1 An impedance transformer for transforming an arbitrary impedancerinto any other desired impedance, comprising a pair of concentric transmission line end sections differing in length by an odd multiple of a quarter-wavelength, means connecting said arbitrary impedance to one of said sections, a quarter Wavey concentric transmission line section, and an adjustable shortcircuited concentric transmission line section formed concentric with and connected in series with each of said end sections and to said quarterwave section, whereby said arbitrary impedance may be transformed to said desired impedance by adjusting said short-circuited sections.

2. An impedance transformer for transforming an arbitrary impedance into any other desired impedance, comprising a pair of concentric transmission line end sections, means connecting said arbitrary impedance to one of said sections, a central concentric line transmission section, and an adjustable short-circuited concentric transmission line section. connected in series between each of said end sections and said central section, whereby said arbitrary impedance may be transformed into sai-d desired impedance by adjusting said two adjustable short-circuited sections.

3. An impedance transformer as in claim 2 wherein each of said adjustable short-circuited concentric transmission line sections comprises lan adjustable plunger, means forming sliding contact between said plunger and the conductors of said section, an-d means for transforming the resistances of said contact to low impedancesv whereby the effects of said contact resistances are minimized.

4. An impedance transformer for transforming an arbitrary impedance into any other desired impedance, comprising a pair of fixedly separated concentric transmission line end sections, means for connecting said arbitrary impedance to one of said sections, a central concentric transmission line section, and an adjustable shortcircuited concentric transmission line section connected in series between the outer conductor of each of said end sections and the outer conductor of said central section, whereby said arbitrary impedance may be transformed into said desired impedance by adjusting said adjustable line sections. y

5. An impedance transfonmer for transforming an arbitrary impedance into any other dearbitrary impedance may be transformed into said desired impedance by adjusting said reactances. I

6. An impedance transformer for transforming an arbitrary impedance to another desired impedance, comprising a section of transmission line connected to said arbitrary impedance, a pair of concentric transmission lines connected in shunt to said'flrst section and spaced a quarter-wavelength apart therealong, and means for independently adjusting the lengths of said shunt lines, whereby said desired impedance may be derived at the other end of said first section.

7. An impedance transformer for transforming an arbitrary impedance into any other desired impedance, comprising fixed concentric transmission -line means for transforming said arbitrary impedance into a first transformed impedance, adjustable reactance means for transforming said first transformed impedance into a second transformed impedance, a second xed concentric transmission line means for transforming said second impedance into a third transformed impedance, a second adjustable reactance means for transforming said third impedance into a fourth transformed impedance, a third xed concentric transmission line means for transforming'said fourth impedance into a fifth transformed impedance, a third adjustable reactance means for adjustably transforming said fifth impedance into a sixth transformed impedance, a fourth fixed concentric transmission line means for transforming said sixth impedance into a seventh impedance, and means for simultaneously adjusting twoof said adjustable reactance means, whereby said seventh impedance may be adjusted to be equal to said desired transformed impedance.

8. An impedance transformer for transforming an arbitrary impedance into any other desired impedance, comprising a main section of concentric transmission line, three further sections of concentric transmission line connected in shunt to said main section, and means for adjusting the reactance of each of said further sections,v whereby said arbitrary impedance connected at one end of said main section may be transformed to said desired impedance at the other end of said main section by adjustment of said reactances.

9. An impedance transformer as in claim 8 comprising means for simultaneously adjustingy impedance into a first transformed impedance,

adjustable reactance means for` transforming said first transformed' impedance'into a second transformed impedance, said adjustable means comprising a coaxial line, a moveablevplunger, means forming sliding contact lbetween said plunger and the conductors of said coaxial line,y

and means for transforming the resistance of said contact to a low impedance, a second xed concentric transmission line means for transforming said second transformed impedance into a third transformed impedance, further adjust/J.

able reactance means for transforming said third impedance into a fourth transformed impedance, and a third concentric transmission line means 17 for transforming said fourth impedance into a fth transformed impedance, whereby said fifth impedance may be made equal to said desired impedance by adjustment of said two reactance means.

12. An impedance transformer as in claim 11 wherein said reactance means are shunt connected to said concentric line means.

13. An impedance transformer for transforming an arbitrary impedance into a desired impedance, comprising fixed concentric transmission line means for transforming said arbitrary impedance into a first transformed impedance, adjustable reactance means series-connected to said concentric line means for transforming said first transformed impedance into a second transformed impedance, a second xed concentric transmission line means for transforming said second transformed impedance into a third transformed impedance, further adjustable reactance means for transforming said third impedance into a fourth transformed impedance, and a third concentric transmission line means for transforming said fourth impedance into a fifth transformed impedance, whereby said fifth impedance may be made equal to said desired impedance by adjustment of said two reactance means.

14. An impedance transformer for transforming an arbitrary impedance into a desired impedance, comprising Afixed concentric transmission line means for transforming said arbitrary impedance into a first transformed impedance, adjustable reactance -means for transforming said first transformed impedance into a second transformed impedance, a. second fixed concentric transmission line means comprising a quarter-wave section of concentric transmission line for transforming said second transformed impedance into a third transformed impedance, further adjustable reactance means for transforming said third impedance into a fourth trans'- formed impedance, and a third concentric transmission line means for transforming said fourth impedance into a fifth transformed impedance, whereby said fifth impedance may be made equal to said desired impedance by adjustment of said two reactance means.

15. An impedance transformer for transforming an arbitrary impedance into a desired impedance, comprising fixed concentric transmission line means for transforming said arbitrary impedance into a first transformed impedance, adjustable reactance means for transforming said first transformed impedance into a second transformed impedance, a. second fixed concentric transmission line means for transforming said second transformed impedance into a third transformed impedance, further adjustable reactance means for transforming said third impedance into a fourth transformed impedance, and a third concentric transmission line means for transforming said fourth impedance into a fifth transformed impedance, said rst and third concentric transmission line means comprising concentric transmission line sections differing in length by an odd multiple of a quarter-wavelength, whereby said fifth impedance may 'be made equal to said desired impedance by .adjustment of said two reactance means.

16. An impedance transformer for transforming an arbitrary impedance into a desired impedance, comprising xed concentric transmission line means for transforming said arbitrary impedance into a first transformed impedance, adjustable reactance means for transforming said rst transformed impedance into a second transformed impedance, a second'fxed concentric transmission line means for transforming said second transformed impedance into a third transformed impedance, further adjustable reactance means for transforming said third impedance into a fourth transformed impedance, and a third concentric transmission line means for transforming said fourth impedance into a fifth transformed impedance, said first and third concentric transmission line means comprising concentric transmission line sections differing in vlength by an odd multiple of a quarter-wavelength of the operating frequency, and said second xed concentric transmission line means further comprising a quarter wave section of concentric transmission line, whereby said fifth impedance may be made equal to said desired impedance by adjustment of said two reactance means.

17. Ultra-high frequency apparatus comprising a main section of coaxial transmission line, a plurality of further sections of coaxial transmission lines more than two in number connected in shunt to said main section and spaced equidistantly therealong, means for adjusting the reactance of each of said furthersections, the spacing between successive ones of said plural- -ity of shunt sections being substantially less than one wavelength at the operating frequency, and further comprising means coupling together predetermined ones of said reactance adjusting means for simultaneously adjusting the reactances of said further sections.

WILLIAM W. HANSEN. JOHN R. WOODYARD. MORRIS RELSON.

REFERENCES CITED The following references are, of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,932,448 Clavier Oct. 31, 1933 2,203,806 Wolf June 11, 1940 Re. 20,859 Potter Sept.. 13, 1938 2,132,208 Dunmore Oct. 4, 1938 2,121,855 Buschbeck June 28, 1938 2,106,769 Southworth Feb. 1', 1938 2,284,529 Mason May 26, 1942 1,927,393 Darbord Sept.. 19, 1933 2,226,479 Pupp Dec. 24, 1940 2,373,233 Dow et al Apr. 10, 1945 Certificate of Correction Patent No. 2,438,912. April 6, 1948.- WILLIAM W. HANSEN ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 14, line 10, for Blf read G1 line 59, for the Word its before fully read lle; line 63, strike out and before has; line 67, for electrical length read electrical lengths; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofce.

Signed and sealed this 20th day of July, A. D. 1948.

[IML] THOMAS F. MURPHY,

Assistant Commissioner of Patente, 

